A system for sealing a percutaneous puncture in a vessel may comprise an introducer sheath; and if the system belongs to the class of sealing devices wherein an inner seal is deployed inside the vessel, the distal portion of this introducer sheath extends through the vessel wall and into the vessel. During the introduction phase, the inner seal is folded inside the introducer, and to ensure proper unfolding of the inner seal, the inner seal has to be deployed some distance away from the vessel wall before the inner seal is retracted to be securely seated against the inner surface of the vessel wall. In other words, the distal end of the introducer sheath should be positioned at a desired location inside the vessel, with a known distance from the vessel wall, which, in turn, implies that the position of the vessel wall has to be determined.
An example of such a puncture closure system is disclosed in U.S. Pat. No. 6,090,130. This closure system comprises a vessel locator that includes means for enabling blood from an artery to flow therethrough, so that the position of the artery wall can be determined. Basically, the vessel locator comprises an introducer sheath and a dilator provided with a canal, through which blood can flow from a hole provided in the distal portion of the vessel locator to the proximal portion, where a user can observe a flow of blood out from a hole provided in the proximal portion. In order to correctly position the introducer sheath, the user has to perform several steps. First the introducer sheath is inserted into the artery such that blood can be observed at the proximal end of the introducer sheath. The introducer sheath is then retracted until the flow of blood out of the proximal end just stops, which indicates that the distal end of the introducer sheath has just left the arterial lumen. Thereafter, the introducer sheath is reinserted approximately 10 mm into the puncture to ensure that the distal end of the introducer sheath is at the desired location within the artery. Blood flow should be re-established from the proximal end at this time. From this point, the introducer sheath must be kept fixed.
This known vessel locator and the corresponding way of determining the position of the vessel wall have at least the following disadvantages. It is a messy procedure, with a rather large amount of blood flowing from the distal end of the introducer sheath. Secondly, and more importantly, it can, in praxis, be difficult to exactly determine the position at which the flow of blood just stops, i.e. for some patients the transition from a large flow of blood to essentially no flow of blood is not a readily observable discrete transition but a gradual transition, which makes it difficult to accurately determine the exact position of the vessel wall. Since the determination of the position of the vessel wall is the starting point for the reinsertion of the introducer sheath, the position of the distal end of the introducer sheath suffers from the same uncertainty. Furthermore, the somewhat arbitrary 10 mm reinsertion of the introducer sheath enhances this uncertainty. Finally, it should be noted that a user has to hold the introducer sheath fixedly without any assistance from a natural stop, i.e. the introducer sheath is free to move in the distal direction as well as in the proximal direction.